Okay, I've checked just about everything there is to check now. Wheel cylinders are good, lines are good. Only thing left IS the master. Here's what I'm thinking...
I think the push rod needs to be lenthened. I think the front cylinder is being compressed and getting great pressure to the front (rear wheels) piston but the push rod is stopped before it can push the rear (front wheels) piston. Lengthening the push rod would allow the front and back to both be pressurized.
This is a simple system, there really isn't anything else left to trouble shoot so this week I'll adjust the pushrod and see if that's it. Other than that, there's nothing left to do except go back to the original system or keep trying other master cylinders until I find one that works.